The disclosed invention is directed generally to composite chassis structures for electronic circuits, and more particularly is directed to a hybrid metal matrix composite chassis structure having different metal matrix composite layers metallurgically bonded together.
As electronic circuitry becomes smaller as a result of integrated circuit advances, the amount of power dissipated per unit volume increase while the size of packaging (e.g., box-like containers with external connectors) typically decreases. The net result is increased thermal energy which must be dissipated over a smaller area. The packaging material, therefore, becomes an increasingly significant factor in the over-all performance and reliability of the packaged electronic circuitry.
A further consideration with the increased thermal energy density is unmatched thermal expansion characteristics. For example, an alumina substrate supporting electronic circuitry can be bonded to a planar surface of a circuit package, which typically would comprise a different material such as aluminum. Alumina and aluminum have different coefficients of thermal expansion, and temperature variation would result in mechanical stresses. If the stresses are large enough, the substrate-to-package bond could be fractured outright. Lower intensity stresses could degrade the bond through fatigue over the lifetime of the packaged system. In any event, stresses resulting from expansion mismatch can degrade the bond, increasing thermal resistance in the steady-state operating temperature and shortening the life of the packaged circuitry.